Hydrocyclones are widely used in the metallurgical industry for the separation of particles in a slurry according to their size and/or density, the particles emerging in one of two streams, namely, the underflow or the overflow.
As is well known, the proper operation of a hydrocyclone depends on a suitable rotational motion of slurry inside the cyclone with a core of air along its axis. This rotational motion is still present in the underflow of a cyclone with the result that the combined axial and angular velocities of the underflow stream cause it to adopt the nature of a spray of nearly conical shape. When a hydrocyclone is overloaded, the rotational motion of the slurry in the cyclone is altered such that the angular velocity of the slurry emerging from the hydrocyclone as an underflow stream is small compared with its axial velocity. This causes the air core to be disturbed and a slender rope-shaped discharge or a blockage to result.
Common on-line measurements used in connection with the operation of hydrocyclones are the flowrate and density of the slurry being fed to the hydrocylone and, in some cases, the inlet pressure of such slurry. The inlet pressure has proved to be of little use in the derivation of additional information because it is highly correlated with the feed flow and density measurements.
The actual shape of the hydrocyclone underflow stream is approximately conical, under normal operating conditions, and has therefore a radius at some distance away from the underflow outlet itself. This radius can be sufficient to characterise the shape of the underflow stream. Alternatively, and more conveniently, the shape can be characterised by the angle of flare of the approximately conical stream. This angle varies continuously with changes in the variables associated with the operation of the hydrocyclone.
This feature of the underflow stream has been used, in the past, to control the operation of a hydrocyclone to some extent, or at least to shut it down or provide an alarm when the shape of an underflow stream corresponds to undesirable operation, such as roping.
Thus, for example, there has been described in U.S. Pat. No. 4,246,576 to Grieve et al a monitor which is, in effect, a transition detector, and which provides an outward indication simply of whether the underflow is "normal" or "abnormal". In effect this monitor simply acts as a switch indicating either of two conditions of the underflow.
U.S. Pat. No. 3,114,510 to McCarthy and Curtis describes another form of underflow monitor which simply determines whether or not the shape (angle) of the underflow is between two limits corresponding to "underload" and "overload". In other words the monitor simply detects whether or not the shape of the underflow is anywhere within a desired operating range, but gives no indication as to where in such operating range.
Applicant has already established that the shape (angle) of the underflow stream over a continuous range between chosen limits, can be used in the control of the operation of a hydrocyclone or, alternatively, a milling circuit embodying a hydrocyclone.
Further research and development has now revealed that use of the shape or angle of the underflow stream of a hydrocyclone can in fact be employed in a method and apparatus for actually measuring characteristics associated with the feed, underflow, or overflow streams of a hydrocyclone and, in particular, in particle size, liquid content, and mass flowrate determinations.
It is, accordingly, the object of this invention to provide a method and means for the measurement of a characteristic of any of the feed, underflow or overflow streams of a hydrocyclone wherein the shape (angle) of the underflow stream is employed as one process input to effect measurement of such a characteristic.
It is another object of this invention to provide measurement apparatus which embodies a hydrocyclone and means for measuring the shape (angle) of the underflow stream.